The mammalian eye is a complex organ comprising an outer covering including the sclera (the tough white portion of the exterior of the eye) and the cornea, the clear outer portion covering the pupil and iris. In a medial cross section, from anterior to posterior, the eye comprises features including, without limitation: the cornea, the anterior chamber (a hollow feature filled with a watery clear fluid called the aqueous humor and bounded by the cornea in the front and the lens in the posterior direction), the iris (a curtain-like feature that can open and close in response to ambient light) the lens, the posterior chamber (filled with a viscous fluid called the vitreous humor), the retina (the innermost coating of the back of the eye comprised of light-sensitive neurons), the choroid (and intermediate layer providing blood vessels to the cells of the eye), and the sclera. The posterior chamber comprises approximately ⅔ of the inner volume of the eye, while the anterior chamber and its associated features (lens, iris etc.) comprise about ⅓ of the eye's volume.
The delivery of therapeutic agents to the anterior surface of the eye is relatively routinely accomplished by topical means such as eye drops. However, the delivery of such therapeutic agents to the interior or back of the eye, even the inner portions of the cornea, presents unique challenges. Drugs are available that may be of use in treating diseases of the posterior segment of the eye, including pathologies of the posterior sclera, the uveal tract, the vitreous, the choroid, retina and optic nerve head (ONH).
However, a major limiting factor in the effective use of such agents is actually getting the agent to the affected tissue. The urgency to develop such methods can be inferred from the fact that the leading causes of vision impairment and blindness are posterior segment-linked diseases. These diseases include, without limitation, age-related macular degeneration (ARMD), proliferative vitreoretinopathy (PVR), diabetic macular edema (DME), and endophthalmitis. Glaucoma, which is often thought of as a condition of the anterior chamber affecting the flow (and thus the intraocular pressure (IOP)) of aqueous humor, also has a posterior segment component; indeed, certain forms of glaucoma are not characterized by high IOP, but mainly by retinal degeneration alone.
The present invention relates to the use of Glucocorticoid Derivatives (GDs) that are either selectively designed to possess the ability to be directed to tissue of the posterior segment of the eye, or which possess the ability, when administered to the posterior segment of the eye, to preferentially penetrate, be taken up by, and remain within the posterior segment of the eye, as compared to the anterior segment of the eye. More specifically, the invention is drawn to ophthalmic compositions and drug delivery systems that provide extended release of the Glucocorticoid Derivatives to the posterior segment (or tissue comprising within the posterior segment) of an eye to which the agents are administered, and to methods of making and using such compositions and systems, for example, to treat or reduce one or more symptoms of an ocular condition to improve or maintain vision of a patient.
Glucocorticoids are one of the three major classes of steroid hormones, the other two being the sex hormones and the mineralocorticoids. The naturally occurring glucocorticoids include cortisol (hydrocortisone), which is essential for the maintenance of life. Cortisol is a natural ligand to the glucocorticoid nuclear receptor, a member of the steroid superfamily of nuclear receptors, a very large family of receptors that also includes the retinoid receptors RAR and RXR, the peroxisome proliferator-activated receptor (PPAR), the thyroid receptor and the androgen receptor. Among other activities, cortisol stimulates gluconeogenesis from amino acids and lipids, stimulates fat breakdown and inhibits glucose uptake from muscle and adipose tissue.
Glucocorticoids can therefore be distinguished by their activity, which is associated with glucose metabolism, and by their structure. All steroid hormones derive their core structure from cholesterol, which has the following structure and numbering scheme.

Glucocorticoids are large multiringed derivatives of cholesterol; the characteristics comprising a hydroxyl group at C11, and/or a double bond between C4 and C5. The double bond between carbons 5 & 6 is not an essential part of a glucocorticoid, nor is the identity of any particular R group at C17.
Corticosteroids are steroid hormones released by the adrenal cortex; they comprise the mineralocorticoids (the only naturally occurring mineralocorticoid is aldosterone) and the glucocorticoids. The term “corticosteroid” is sometimes used to mean glucocorticoid, and unless specifically indicated otherwise, this will be the meaning in this patent application. Exemplary glucocorticoids include, without limitation, dexamethasone, betamethasone, triamcinolone, triamcinolone acetonide, triamcinolone diacetate, triamcinolone hexacetonide, beclomethasone, dipropionate, beclomethasone dipropionate monohydrate, flumethasone pivalate, diflorasone diacetate, fluocinolone acetonide, fluorometholone, fluorometholone acetate, clobetasol propionate, desoximethasone, fluoxymesterone, fluprednisolone, hydrocortisone, hydrocortisone acetate, hydrocortisone butyrate, hydrocortisone sodium phosphate, hydrocortisone sodium succinate, hydrocortisone cypionate, hydrocortisone probutate, hydrocortisone valerate, cortisone acetate, paramethasone acetate, methylprednisolone, methylprednisolone acetate, methylprednisolone sodium succinate, prednisolone, prednisolone acetate, prednisolone sodium phosphate, prednisolone tebutate, clocortolone pivalate, fluocinolone, dexamethasone 21-acetate, betamethasone 17-valerate, isoflupredone, 9-fluorocortisone, 6-hydroxydexamethasone, dichlorisone, meclorisone, fluprednidene, doxibetasol, halopredone, halometasone, clobetasone, diflucortolone, isoflupredone acetate, fluorohydroxyandrostenedione, beclomethasone, flumethasone, diflorasone, clobetasol, cortisone, paramethasone, clocortolone, prednisolone 21-hemisuccinate free acid, prednisolone metasulphobenzoate, prednisolone terbutate, triamcinolone acetonide 21-palmitate, prednisolone, fluorometholone, medrysone, loteprednol, fluazacort, betamethasone, prednisone, methylprednisolone, triamcinolone hexacetonide, paramethasone acetate, diflorasone, fluocinolone and fluocinonide, derivatives thereof, salts thereof, and mixtures thereof. Some of these compounds are GDs, as defined in this patent application, and others are prospective parents of such GDs.
In 1950 the Nobel Prize for Medicine was awarded to Hench, Kendall and Richenstein for their work concerning adrenal (naturally occurring) and synthetic glucocorticoids. Since that time these compounds including, without limitation, hydrocortisone and the synthetic glucocorticoids dexamethasone and prednisolone have been a valuable part of the physician's arsenal of weapons to fight inflammation, inflammatory diseases and conditions such as acute asthma.
The glucocorticoid receptor (GR) is found in almost all tissues of the mammalian body. The nuclear receptors, including the glucocorticoid receptor, are ligand-dependent transcription factors that, when activated, bind to chromosomal DNA and initiate or inhibit the transcription of particular genes. As a result, steroids have myriad effects on various systems of the body.
Historically, the short-term systemic or topical use of glucocorticoids has been largely free of serious side effects, and the therapeutic effects of such use are sometimes quite miraculous, particularly in treating diseases related to inflammation, such as arthritis and the like. However, because of the diverse and somewhat poorly characterized effects these compounds have, prolonged use of glucocorticoids, particularly prolonged systemic exposure to these agents, can give rise to a variety of sometimes serious side effects such as glucose intolerance, diabetes, weight gain, osteoporosis, and fat redistribution, as well as frailty and skin thinning.
The topical use of steroids in the treatment of ophthalmic conditions (particularly ocular inflammation) is also well known. Clinicians have found topical administration of steroids to be safe and effective for short-term use in the treatment of conditions of the anterior chamber of the eye. For moderate to severe inflammation loteprednol etabonate 0.5% (Lotemax®), prednisolone acetate (Pred Forte), prednisolone sodium phosphate (Inflamase Forte®) and rimexolone (Vexol®) have been used with success, while the fluorometholones are prescribed for mild to moderate inflammation—additionally, dexamethasone and hydrocortisone are also used for topical ocular use. Triamcinolone (Kenalog 50®—approved for dermatological use) has been successfully used as an off-label medication for intravitreal injection for the treatment of macular edema. All of the above-mentioned topical steroid preparations are designed and/or used mainly for superficial or anterior segment inflammation. However, topical application of steroid drugs does not result in significant concentrations of the drug entering the posterior segment. Indeed, only a minute fraction of the drug topically applied to the surface of the eye ends up within the eye, with the majority of what drug does enter the eye remaining contained within the anterior segment. Retisert®, is a non-biodegradable implant for delivery to the posterior segment. It comprises fluocinolone acetonide, and has been approved for the treatment of chronic noninfective posterior uveitis. Retisert® has also been associated with 90.3% of study eyes developing cataracts, necessitating surgical removal. See Hudson, Henry L., Retinal Physician July 2005 (www.retinalphysician.com/article.aspx?article=100098), incorporated herein by reference. Some ophthalmologists have recently made use of the triamcinolone acetonide suspension Kenalog® 40 by injecting into the vitreous of patients suffering from conditions including, without limitation, cystic macular edema, diabetic macular edema, and wet macular degeneration. The few steroids, such as dexamethasone and triamcinolone acetonide that have been reported to be used intravitreally tend to migrate by diffusion to anterior segment tissues, which can cause serious and unwanted side effects.
Additionally, in May 2003 Oculex Pharmaceuticals announced that preliminary findings from a clinical trial testing a biodegradable intravitreal implant containing 700 μg of the corticosteroid dexamethasone showed that the implant, having the trade name Posurdex®, was highly effective in improving vision in patients suffering from persistent macular edema.
When treating conditions of the posterior segment with steroids it is particularly preferable to reduce the exposure of anterior segment tissues to steroids—long term use of steroids can lead to extremely high incidence of lens cataracts, ocular hypertension, and steroid-induced glaucoma. In part, the present invention is drawn to methods of treating a variety of conditions of the posterior segment including (without limitation): cystic macular edema, diabetic macular edema, diabetic retinopathy, uveitis, and wet macular degeneration, by the administration of GDs, including C17- and/or C21-substituted GDs, to specifically target the tissue of the posterior segment of the eye, and to resist migration to the anterior segment. In other embodiments the invention is drawn to compositions comprising such glucocorticoid components and to methods of administrating such glucocorticoids.
In a particularly preferred embodiment a composition comprising one or more GD is administered directly to the posterior segment by, for example, injection or surgical incision. In a further embodiment the composition is injected directly into the vitreous humor in a fluid solution or suspension of crystals or amorphous particles comprising a GD compound. In another embodiment the composition is comprised within an intravitreal implant. The GD may, without limitation, be comprised in a reservoir of such implant, may be joined to a biodegradable implant matrix in such a manner that it is released as the matrix is degraded, or may be physically blended with the biodegradable polymeric matrix.
Additionally, while less preferred, a GD of the present invention may be administered to the posterior segment indirectly, such as (without limitation) by topical ocular administration, by subconjunctival or subscleral injection.
The GDs of the present invention all possess certain properties in accord with the present invention. First, the GD should possess a relatively slow dissolution rate. By “relatively low dissolution rate” is mean a dissolution rate from the solid to the vitreous liquid phase, which is less than that of triamcinolone acetonide preferably 50% or less of the dissolution rate of triamcinolone acetonide, even more preferably 25% or less than the dissolution rate of triamcinolone acetonide, 10% or less than that of triamcinolone acetonide.
Secondly, the GD should possess a relatively low solubility in the vitreous humor. By “relatively low solubility” is mean a solubility which is less than that of triamcinolone acetonide, preferably 50% or less of the dissolution rate of triamcinolone acetonide, even more preferably 25% or less than the dissolution rate of triamcinolone acetonide, or 10% or less than that of triamcinolone acetonide.
In another measurement of solubility, the GD used in the present invention has an aqueous solubility less than about 21 mg/ml, preferably less than about 10 mg/ml, even more preferably less than about 5 mg/ml, or less than about 2 mg/ml, or less than about 1 mg/ml, or less than about 0.5 mg/ml or less than about 0.2 mg/ml or less than about 0.14 mg/ml at room temperature and atmospheric pressure (sea level).
Finally, the GD should be highly lipophilic so as to partition well into the membranes of retinal tissue and quickly achieve a high local concentration of GD in retinal tissue. This means that a GD has a lipophilicity (log P, where P is the octanol/water partition coefficient) of greater than 2.53, or greater than 3.00, or greater than about 3.5 or greater than about 4.00, or greater than about 4.20 at room temperature and atmospheric pressure (sea level).
While a most preferred GD possesses all of these properties, a GD may possess less than all such properties so long as it possesses the property of remaining therapeutically active in the posterior chamber when delivered intravitreally, while not being present in therapeutically effective concentrations in the anterior chamber.
The vitreous chamber bathes the posterior surface of the lens and is connected to the anterior chamber via a fluid channel that encircles the lens and continues through the pupil. Solutes (including solubilized glucocorticoids) in the vitreous may diffuse anteriorly to the lens, or around the lens to the anterior chamber outflow apparatus (the trabecular meshwork, Schlemm's canal), thereby causing steroid-induced cataracts, ocular hypertension or glaucoma.
The present inventors have found that steroids that are only sparingly soluble in vitreal fluid and that have a slow dissolution rate from the solid to the soluble form do not migrate well to the anterior segment. While not wishing to limit the scope of the invention by theory, and only as an illustration, the Applicants believe that the GDs of the present invention lack sufficient diffusional force due to their lack of solubility in the vitreous to move the soluble steroid through the indicated path to the anterior chamber. The lipophilicity of the GDs of the present invention, at the same time, encourages their partition from the aqueous vitreous fluid to the lipid bilayer of the retinal cell membranes. This is thought to create a low-level intravitreal flow of the GD from vitreous to retina, at a concentration sufficient to provide therapeutic benefit to the retinal tissue, but at a low enough level to confer substantially reduced exposure to the lens and anterior segment tissues.